Microscopic printing ey planographic means



Feb. 7, 1956 A. BONI 2,733,655

1 MICROSCOPIC PRINTING BY PLANOGRAPHIC MEANS Filed May 15, 1951'INVENTOR.

A TTORN EV United States Patent MICROSCOPIC PRINTING BY PLANOGRAPHICMEANS Albert Boni, Chester, Vt., assignor to Readex MicroprintCorporation, New York, N. Y., a corporation of New York a ApplicationMay 15, 1951, SerialNo. 226,505 Claims. (Cl. 10-1----149) This inventionrelates to the art of planographic printing and has for its principalobject the provision of a process by which lithographic or otherplanographic print of extremely small size can be produced on paper orother sheet material, with sufiicient clarity to be read with the use ofa simple optical enlarger or viewer.

There are many instances in which it would bedesirable to makemicroscopic reproductions of plano graphic printing, as, for example,when space requirements do not permit maintaining extensive records,publications, etc., having print ofordinary sizes. In the past, manyattempts have been made to provide such reproductions, as by makinggreatly reduced photographs of printed matter. The results of theseattempts, however, have involved limitations, particularly with respectto cost, which either restrict greatly the field of commercial use ofthe technique or make it unsuitable for any commercial-use.

The principal difliculty encountered in microscopic printing with ink isthe lack of sharpness in the definition of the small printed characters,so that they take on a blurred appearance when viewed through theoptical enlarger. That is, the microscopic characters appear to have amottled texture and jagged or feathery edges, which may be referred toas a low 'fidelity efiect. This efiect becomes more pronounced thegreater the reduction in the size of the characters, and has been alimiting factor in the extent to which the printing can be reduced insize as compared with ordinary printing. For example, a reduction offive diameters in ten-point type has usually be considered the maximumreduction possible without an intolerable sacrifice in the clarity ofthe print.

I have discovered a process for high-fidelity microscopic, planographicprinting which enables the characters to be made much smaller than hasbeen possible commercially heretofore and still retain their sharpnesseven when magnified 1S and more diameters. According to my process, theprinting is made directly upon the paper or other sheet from alithographic or pianographic printing plate having ink-receptive imagesof small size. However, the ink is applied repeatedly to the plate priorto each printing impression on-the paper, with only a light coating ofink at each application to the plate, and the printing impression on thepaper is made by the plate under a pressure considerably in excess ofthose conventionally used in planographic printing. in other words, themicroscopically printed characters are made up of accuratelysuperimposed, relatively thin ink layers built up on the planographicprinting plate and then impressed upon the sheet "by heavy pressure. Thethickness or heaviness of the ink coating applied to the printing plateat each of the repeated inkings of the plate is determined by the numberof the repeated ink-ings and the amount of ink which can be appliedunder the heavy printing pressure without causing smudg'ing or"spreading of the ink on :the paper. That is, when the inking of theplate is 'repeatedonly 2,733,655 1 C3 Patented Feb. 7, 1956 once, eachink coating applied to the plate will generally be heavier than whenseveral repeated inkings are made; and when heavier printing pressuresare used, the ink coatings will generally be thinner and applied moretimes to the plate. The more times the inkings of the plate are repeatedbefore each printing impression, and hence the lighter the ink coatingat each application of ink to the plate, the finer will be the ultimatedetail obtainable in the microscopic printing.

The repeated inkings can be made conveniently with conventionalduplicating machines of the direct printing type. I have found that theDavidson Dual Duplicator, equipped for direct printing, can be used forthis purpose, since it permits easy control of the thickness of the inkcoating applied to the printing plate, enables repeated inkings of theprinting plate before the impress'ion is made on the paper from theplate, and allows adjustment of the printing pressure to the relativelyhigh range required by my process. Since this Davidson machine is"well-known in the printing art, it is not described or illustrated indetail here. Briefly, when the Davidson machine is used in the practiceof the prese'nt invention, it is set .up for direct printing so that theblanket cylinder constitutes the impression cylinder or platen, and thesegment for holding the lithographic or other planographic printingplate bearing the microscopic .in'kereceptive images is attached to thelarge cylinder in place of the impression segment. The lead edge of thepaper is gripped by grippers operating on continuous chains, rather thanon a cylinder, and the grippers are opened by a cam which determines thepoint at which the paper is released after passing between thecylinders, apparatus of this type being disclosed in W. W. DavidsonPa-tents -No. "2,436,165 of February 24, 1948', and No. 2,374,668 of May1, 1945. The paper may be inserted into and removed from the grippersmanually at the beginning and .end of the complete operation. Thethickness of the ink coating applied to the printing plate at eachrevolution may regulated in any conventional manner, by adjusting thepressure of the doctor blade on 'the ink fountain roller. The pressureof the printing plate .or large cylinder against the blanket cylindermaybe adjusted in the usual manner by a lever movement "which yaries thespacing between the parallel axes of the cylinders. The inter-cylinderpressure is .a .direct function :of the distance through which thisspacing is decreased after initial contact between the plate andblanket. Thus, if the setting of the lever gives a 3 thousandthscof aninch movement of the plate against the blanket, after the initialcontactfthe intercylinder or printing pressure is referred :to as 3thousandths of an inch.

The pressure :at which the printing impression is made, following therepeated inkin gs of the plate, is a critical .factor in :obtainingfineness of detail of the microscopic printing. Atthe pressuresordinarily used-in planographic printing =(about2 or '3 thousandths ofan inch), there is no noticeable or appreciable improvement in thefineness .of detail when making repeated inkings. I have discovered thatthere is no appreciable improvement in this respect until the pressureis increased to about 18 'thousandthsof an'inch. For best results, thepressure should be within 'the range of 28 to '35 thousandths of -aninch. 1 have found that the above-specified pressures are applicable forcommercially available blankets of different degreesof hardness,evidently because the blankets are very thin (in the-order of 78 thousandths of an inch).

I have found that the type of printing plate used in the process is alsoa factor affecting the clarity of fineness of detail .of the microscopicprinting. For best results, the printing .plate should be a lithographicplate having the finest possible grained surface, preferably so fine asto give the surface a substantially mirror-like surface.

The process can be practiced with good results when printing oncommercially available paper stock. I have found that the mostsatisfactory results are obtained when using coated papers, such asKromekote, which isa product of Champion Paper and Fiber Company, ofHamilton, Ohio, the coating of thispaper being nonporous and showing nosurface roughness or hills and valleys under a lX lens, and being ofuniform thickness throughout its area.

The new process produces'striking'results in the fineness of detail ofthe microscopic printing when viewed through a magnifying glass orenlarger. For example, when a direct printing'plate is made to duplicatea full page of The New York Times (which uses 6 point type) with areduction of 717 /2 diameters, the microscopic printing from this platein accordance with my invention can be read very easily with amagnifying glass giving a corresponding enlargement. In fact, theprinting has extremely fine detail when viewed through the enlarger. Inthis manner, I have been able to reprint, microscopically, 25

pages of The New York Times on a sheet space measuring only 5 inches by7%' inches, with excellent results in the clarity of the print whenviewed through the enlarger. From this example, it will be appreciatedthat the new process can be used to greatadvantage for many purposes,particularly in view of its simplicity, the fact that it can bepracticed with conventional duplicating equipment, and the fact that itdoes not require expensive materials.

In the accompanying drawing-I have illustrated schematically anapparatus for use in carrying out the process. As there shown, theapparatus comprises a plate cylinder 1 mounted for rotation on its axisby fixed bearings at each end, one of the end bearings being shown at 2.On the periphery 'of the-cylinder is a lithographic printing plate 3 inthe form .of a segment, which is releasably secured to the cylinder inany desired manner. This plate carries the microscopic inkareceptiveimages and is preferably a lithographic plate having a smooth,substantially grainless surface. A blanket or impression cylinder 4 ismounted for rotation adjacent andparallel to the plate cylinder on axialend bearings, one of which is shown at 5. These bearings, however, aremovable on arms slidable in fixed bushings, thesupporting arm for thebearing 5 being shown at 6 and its fixed bushings at 77a. To

each arm 6, intermediate itsbushings 7-7a, a lever 8 is pivotallyconnected at its lower end, the lever being adapted to swing on a fixedpivot 9 above the arm. By swinging the levers 8, the impression cylinder4 may be moved bodily toward or away. from the plate cylinder 1, to movethe cylinders into and out of engagement. levers 8 also serve .to adjusttheintercylinder pressure to and within the range previously specified.When the pressure adjustment has been made, the pressure is maintainedby nuts 10-1011 threaded on each arm 6 and adapted to be tightenedagainst the ends of its bushing 7a. As previously mentioned, thepressure is here considered as the distance (in thousandths of an inch)through which the cylinder 4 is moved toward and against the cylinder 1after initial contact between the periphery of cylinder 4 and theperiphery of plate 3.

The impression cylinder 4 is of the same diameter'as the plate cylinder1, and the two cylinders are driven at equal speeds in oppositedirections (as shown by the arrows) by any suitable or conventionaldriving mechanism (not shown), such as the mechanism used in theaforesaid Davidson machine, which permits adjustment of the spacingbetween the axes of the cylinders. The impression cylinder 4 has aresilient covering or blanket and may be the type of cylinder referredto as the blanket cylinder in' the Davidson machine, the blanket beingpreferably of the standard'hard classification. The paper is held on theblanket cylinder 4 by a gripping device .11, which may be ofconventional form to clamp the paper The ' along itsleading edge againstthe periphery of cylinder 4.

This gripping device, as shown, is hinged to the cylinder 4 at 11a andits lagging or free end is held in its clamping position againstcylinder 4 by a spring 12. The gripping device may be lifted against thespring 12 to permit insertion or removal of the paper.

During the initial rotation of the cylinders 1 and 4, the lovers 8 areadjusted to provide a space between the cylinders, so that no printingimpression will be made by the printing plate 3. During this initialrotation of the spaced cylinders, a thin coating of ink is appliedrepeatedly to the plate 3 by ink transfer rolls 13 which receive inkfrom a fountain or reservoir 14. The thickness of each ink coating maybe regulated in any suitable manner, as by adjusting the pressure of thedoctor blade 17 against the ink roll 13 in the fountain 14, to squeezemore or less of the ink from this roll. Before each application of inkto the plate, the plate is dampened with the usual moistening solutionapplied from a reservoir 15 by transfer rolls 16. During each revolutionof the cylinders, a light coating of ink is applied to the plate 3 fromthe ink rolls 13, after moistening of the plate by the rolls 16. After.the desired number of repeated inkings (preferably 3-5),

the plate is ready for the printing impression. The latter is eiiectedby operating the levers 8 to engage the cylinders and adjust theinter-cylinder pressure to the relatively high range, as previouslydescribed. The paper may be fed to and released from the gripper 11manually, or it may be fed and released automatically, after therequired number of cylinder rotations under the ink rollers 13. Forexample, the stationary cams for releasing the gripper at the feedingstation in the Davidson Dual Duplicator, may be made movable so thatthey can be projected into their operating positions only after thedesired number of rotations of the cylinders.

'The thickness of each ink coating applied to the plate 3 by thetransfer rollers 13 is, as previously mentioned, considerably less thanis used normally, that is, with only asingle application of ink to theplate prior to each printing impression. In general, the thickness ofeach of the superimposed ink coatings on the plate will be roughly l/nof the thickness normally used, where n is the number of thesuperimposed inkings. When the number of these inkings is 4, forexample, the thickness of the ink coating applied to the plate at eachcylinder revolution will generally be about A of the ultimate thicknessof the composite super-imposed ink layers on the plate.

I claim:

1. A planographic printing process for producing fine print on asheet'with the use of a rotary planographic printing plate, a parallelrotary cylinder and a resilient blanket, which comprises moistening andapplying a light coating of 'ink repeatedly to the plate beforeimpressing ,the plate against the sheet, the thickness of each inkcoating being generally l/n of the ultimate thickness of the .compositesuperimposed ink layers applied to the plate,

where n is the number of said ink coating applications, and then passingthe sheet between the cylinder and plate, to make the printingimpression on the sheet, while maintaining between the cylinder andplate a heavy pressure equal to the pressure obtained by displacing theaxis ,of the plate toward the parallel axis of the cylinder throughmaking a printing impression on the sheet from the plate 'under'a heavypressure obtained by moving the plate against the blanket through adistance of at least about 18 thousandths of an inch, after initialcontact of the plate and blanket.

3. A process according to claim 2, in which said pressure is obtained bymoving the plate against the blanket through a distance of 28 to 35thousandths of an inch, after initial contact of the plate and blanket.

' 4. A process according to claim 2, in which the number of said inkcoatings is between 3 and 5.

5. A process according to claim 2, comprising also the step of formingthe printing plate from a smooth, substantially grainless lithographicplate.

6. A process according to claim 2, in which said pressure is obtained bymoving the plate against the blanket through a distance of 28.to 35thousandths of an inch,

, after initial contact of the plate and blanket, said printing platebeing formed from a smooth, substantially grainless lithographic plate.

7. A planographic printing process for producing fine print on a sheetwith the use of a planographic printing plate and a resilient blanket,which comprises moistening the plate and coating it with a layer of ink,and then pressing the plate against the sheet on the blanket under aheavy pressure equal to the pressure obtained by displacing the plateagainst the blanket through a distance of at least .018",-after initialcontact of the plate and blanket, to make a printing impression on thesheet from the plate.

8. In the production of fine printing on a sheet with the use of asmooth, substantially grainless lithographic printing plate and aresilient blanket, the process which comprises forming smallink-receptive images on the plate, moistening and making repeatedinkings upon the printing plate while maintaining the plate out ofcontact with the sheet, the thickness of each inking being generally l/nof the ultimate thickness of the composite superimposed inkings, where nis the number of said inkings, and then pressing the plate against thesheet under a heavy pressure equal to the pressure obtained bydisplacing the axis of a rotary printing plate toward the parallel axisof a rotary resilient blanket cylinder through a distance of at leastabout 18 thousandths of an inch, after initial contact of the plate andcylinder, whereby the print is built up from thin, superimposed inklayers from the plate.

9. A planographic direct printing process for producing fine print on asheet with the use of a planographic printing plate and a resilientblanket which comprises moistening the plate and coating it repeatedlywith a thin layer of ink before contacting the plate with the sheet, thethickness of each ink layer being generally 1/ n of the ultimatethickness of the composite superimposed ink layers, where n is thenumber of said coatings, and then making a printing impression on thesheet directly from the plate under aheavy pressure of at least themagnitude obtained by displacing the axis of a rotary printing platetoward the parallel axis of a rotary resilient blanket cylinder througha distance of about 18 thousandths of an inch, after initial contact ofthe plate and cylinder.

10. A microscopic reproduction of printed matter which comprises asheet, and microscopic inked characters each applied to the sheet as apre-formed layer of ink by coating a moistened planographic printingplate with a layer of ink and then pressing the plate against the sheeton a resilient blanket under a heavy pressure equal to thepressureobtained by displacing the plate against the blanket through a distanceof at least .018", after initial contact of the plate and the blanket.

References Cited in the file of this patent UNITED STATES PATENTS129,176 Savage July 16, 1872 148,530 Waddie Mar. 10, 1874 476,135Elsenhardt May 31, 1892 1,227,557 Cochran et al May 22, 1917 2,040,129Hagelin May 12, 1936 2,046,959 Mehl July 7, 1936 2,302,816 Toland et al2.. Nov. 24, 1942 OTHER REFERENCES Art and practice of printing, volumeIII, Montague, published by Sir Isaac Pitman & Sons, Ltd., London, page151. (Copy in Div. 17, U. S. Patent Ofiice.)

Printing Inks, Ellis, published by Reinhold Publishing Corp., New York,N. Y., page 475. (Copy in Div. 17, U. S. Patent Oflice.)

The Lithographers Manual (Soderstrom) published by Walton PublishingCo., New York, N. Y., pages 186-195 and 301. (Copy in Div. 17, U. S.Patent Oflice.)

